1. Field of the Invention
The present invention relates to a method for fabricating a field emission display (FED) cathode. More particularly, the present invention relates to a method for fabricating a field emission display cathode having a larger emission area.
2. Description of the Related Art
Since the field of multimedia is developing quickly, the user has a great demand for entertainment equipment. Conventionally, the cathode ray tube (CRT), which is a species of monitor, is commonly used. However, the cathode ray tube does not meet the needs of multimedia technology because the cathode ray tube has a large volume. Therefore, many flat panel display techniques such as liquid crystal display (LCD), plasma display panel (PDP) and field emission display (FED) have been recently developed. These display techniques can manufacture thin, light, short and small monitors; thus these techniques have become the mainstream monitor technology for the future.
Since the pixel circuit used in the field emission display is faster than that in the liquid crystal display, the optical response time of the field emission display is shorter. This also means that the field emission display has better display performance.
The field emission display has several advantages. It is thinner (about 2 to 10 cm), is lighter (less than 0.2 kg), has a wider view-angle (larger than 80.degree.), is brighter (more than 150 cd/m.sup.2), has a large working temperature range (about -50.degree. C. to 80.degree. C.), consumes less energy (less than 1 W), etc. Furthermore, the manufacturing costs of the field emission display are low.
The field emission display works in a high vacuum environment. By using a strong electric field, electrons in the field emission array (FEA) are emitted, and the electrons impact electroluminescent materials. A catholuminescence effect occurs, so that an image is formed.
FIGS. 1A through 1D are schematic, cross-sectional views showing the progression of the conventional manufacturing steps for a field emission display cathode.
Referring to FIG. 1A, an epitaxial silicon substrate 10 is provided. An oxide layer (not shown) is formed by thermal oxidation on the epitaxial silicon substrate 10, and then the oxide layer is defined by photolithography to form a patterned oxide layer 12.
Referring to FIG. 1B, a portion of the epitaxial silicon substrate 10 is removed by isotropic wet etching. A thermal process is performed to form an oxide layer 15 on surface of the epitaxial silicon substrate 10.
Referring to FIG. 1C, the patterned oxide layer 12 (FIG. 1B) and the oxide layer 15 (FIG. 1B) are removed to form tips 14, and an oxide layer 16 is formed by chemical vapor deposition to cover the epitaxial silicon substrate 10 and the tips 14. A metal layer 18 is formed on the oxide layer 16, and then a patterned photoresist layer 20 is formed on the metal layer 18. Then, the metal layer 18 is etched with the photoresist layer 20 serving as a mask to expose the oxide layer 16.
Referring to FIG. 1D, a buffer oxide etching process is performed to remove a portion of the oxide layer 16, and then the tips 14 are exposed. The photoresist layer 20 (FIG. 1C) is removed. Now, the tips 14 serve as field emitters, the metal layer 18 serves as a gate and the whole epitaxial silicon substrate 10 serves as a bottom plate, or a cathode plate, of a field emission display.
Moreover, the field emission display includes a top plate (not shown), or an anode plate, wherein the top plate includes a glass plate coated with phosphorus. Spacers are located between the top plate and the bottom plate. The field emitters on the bottom plate constitute field emission arrays. By the electric field supplied by the gate, the field emitter excites electrons to generate an electron beam. The electrons are accelerated by positive voltage of the anode plate, so that the electrons impact the phosphorus on the anode plate to generate a catholuminescence effect.
In the conventional technology, the emitter for the field emission array is designed to have a tip according to a point discharge characteristic. However, electrons are only emitted from the tip portion of each emitter, thus the amount of electrons is restricted. As a result, each pixel of the field emission display must comprise hundreds of emitters to produce enough electron flow for impacting the phosphorus on the anode plate to generate the catholuminescence effect. As a result, the area occupied by the field emission array is large. Furthermore, the emitter in the conventional technology is formed on the epitaxial silicon substrate. Because of the uniformity of the epitaxial silicon, it is difficult to manufacture large-size displays.